Why avoid guppies? I breed my own and never had an issue with feeding my other fish. personally i don't like mealworms.. they're hard exoskeleton is almost impossible to digest, and can be sharp enough imo to do internal damage, not to mention the mandibles on these bugs if ingested still alive could do major internal damage to the fish before death of both worm and fish. and unless you gut-load them first, the nutritional value is not imo, ime any better or worse then other feeders.
crickets, earthworms, home bred fish. are the only live foods I generally use. Otherwise QTing any bought feeder fish. wax worms are also a good treat, but I've been told they generally have a high phosphate value and low calcium level. which personally is not worth the risk particularly to my juvie fish for proper bone development. There is also a list around here somewhere where oddball iir listed the nutritional values of most feeder type creatures.
My Senegels get earthworms/nightcrawlers and I am more then happy with the results, you can also try frozen silversides. My needlenose only takes live and I've fed him mainly on QTed rosy minnows, and platies,guppies,mollys I've bred myself. He will also take crickets, but no pellets.
If you're going to try mealworms, I strongly suggest chopping their heads off before feeding. I've seen them chew their way threw reptiles, so have little doubt they are capable of doing it to fish. Most fish do chew their food though. lol. But it is a precaution. I know some people have prolly been feeding them for years, w/out any problems.